May 17, 2011 | General

Combining Residuals To Manufacture Topsoils

topsoil blend for applicationBioCycle May 2011, Vol. 52, No. 5, p. 24
After a flood stripped five acres of farm fields of its topsoil, a blend of short paper fiber, biosolids and sand was applied at an 8-inch depth, seeded and fertilized resulting in high yields of hay.
Shelagh Connelly and Andrew Carpenter

IN October 2005, several days of heavy rain in southwestern New Hampshire caused severe flooding in the Cold River and the surrounding watershed. In one tributary, Warren Brook, an unintentionally dammed drainage structure, holding back a temporary lake, gave way, causing a wall of water to wipe out several homes and roads downstream. The Wilson Farm, owned by Alstead, New Hampshire residents Gene and Bobbie Wilson, was directly in the path of this destructive force.
In addition to losing their barns and farm equipment in the flooding, the five acres of fields that the Wilson’s owned adjacent to Warren Brook were entirely stripped of topsoil; only the cobbly subsoil remained. As Bobbie Wilson noted, the flood and its aftermath “has just been devastating.” Four years later, after a long process of working with several state and federal agencies, and ultimately, private businesses, the Wilson’s were able to restore their lost farm soil with a fertile manufactured topsoil composed of locally available residuals and sand.
In the two years that followed the flood, the Wilson’s were provided very limited assistance for any reconstruction, and ended up depleting all of their personal savings to rebuild their house and barns. While the U.S. Army Corps of Engineers rerouted the course of Warren Brook through the property, no federal assistance was available to replace the topsoil lost in the flooding. Persistent follow up by Bobbie Wilson eventually paid off when the Governor’s office contacted the state Department of Agriculture, which in turn contacted Resource Management, Inc. (RMI), a local organic waste recycling company, to determine if RMI’s manufactured topsoil would be a good fit for restoration of the Wilson’s fields.
before and after topsoil blend application
RMI has been manufacturing topsoil since 1995 for use in disturbed land reclamation projects. It typically consists of short paper fiber, biosolids and mineral components, such as bank-run sand, crusher fines or other low value soil-like materials. Short paper fiber is a by-product of the paper manufacturing process and consists primarily of wood fiber, clay and lime. Due to its low nutrient and trace metal content, short paper fiber can be used at high rates within a topsoil blend to provide ample organic matter without an excess of nutrients or metals. Its high wood fiber content provides a very high C:N ratio (typically over 75:1). Biosolids are used at lower rates within RMI’s manufactured topsoil to provide a slow release form of nitrogen (helping to lower the C:N ratio of the blend) while also providing phosphorus, sulfur and micronutrients that are otherwise found at low levels in the short paper fiber and mineral components of the topsoil. The biosolids also appear to help kick-start biological activity in what is otherwise a relatively sterile medium.
The physical properties of the wood fiber, along with the high organic matter content and water-holding capacity of the manufactured soil, yield exceptional erosion resistance on slopes as steep as 2:1. Consequently, the first uses of the material were primarily for revegetating steep sites, such as capped landfills and reclaimed mines.
In the past eight years, RMI has focused on converting disturbed land to productive agricultural fields. During this transition, the topsoil blends have remained largely unchanged with the exception of adding supplemental residuals and fertilizers to create a balance of fertility more suited to agriculture. For instance, potassium and magnesium are added to the blends to help balance the high levels of calcium contributed by the short paper fiber.
spread topsoil
In New Hampshire, residuals regulations, overseen by the Department of Environmental Services (DES) require site specific permits for land receiving manufactured topsoil containing short paper fiber and biosolids. These sites, as well as facilities where the topsoil is manufactured (blended and stockpiled), also typically require groundwater monitoring. The permitting process is extensive, time consuming, costly and includes several public notification procedures. While the DES, the state Department of Agriculture, RMI and the Wilson’s all agreed that the manufactured topsoil would be a natural fit for restoring the farm fields, the standard permitting procedure for this project would not work with the budget (which had to be no cost to the Wilson’s) and desired time frame for restoring the land. Additionally, the setbacks within the regulations would rule out use of the manufactured topsoil for most of the impacted land, which was adjacent to Warren Brook.
Ultimately, the permitting process was streamlined in a manner that kept the project affordable and timely while providing the environmental protections intended by the DES residuals regulations. For example, the regulations allow portions of DES rules to be waived provided that alternative operations or management strategies are in place to provide equivalent environmental protection. For the Wilson Farm restoration project, the management practices in place that allowed for waiving the groundwater monitoring, site specific permitting, setback requirements and slope restrictions, included the following:
• Stockpiling, mixing and blending topsoil ingredients, including short paper fiber and biosolids, was confined to a two-month period (July and August) which typically corresponds to a drier portion of the year in New England.
• A detailed erosion and odor control plan was developed that included silt fence placement in areas close to Warren Brook (separating the area of application from the buffer for the brook)
• Surface water monitoring upstream and downstream of the site by DES
• A requirement that topsoil placement and seeding occur immediately following blending
• Monthly inspections of the project by DES during topsoil manufacturing and placement until vegetation was established on the manufactured topsoil.
While the minimum setback to Warren Brook was decreased to 35-feet, setbacks to drinking water sources for this project were consistent with existing DES regulations. The fields that would be receiving the manufactured topsoil were not suitable for stockpiling and blending operations. A sand and gravel operation in the neighboring town of Langdon, with an inexpensive source of sand, was identified as the best location for topsoil manufacturing. The short paper fiber came from two paper mills (Monadnock Paper Mills in Bennington, NH and Putney Paper Company in Putney, VT), both within 30 miles of the Wilson Farm. The biosolids came from Concord, the capital of New Hampshire. The Concord biosolids were treated to Class A standards.

Nitrogen management in manufactured topsoils made from fresh (uncomposted) organic matter sources requires careful recipe development. A low C:N ratio in the blend of residuals within the topsoil can result in excessive nitrogen mineralization with the potential for significant nitrate leaching. On the other hand, a manufactured topsoil with a high C:N ratio can cause extended, microbially-induced nitrogen immobilization resulting in poor crop response, in some cases for several years. In order to protect groundwater from nitrate leaching, DES mandated that the topsoil have a minimum C:N of 35:1, a maximum total nitrogen loading of 2,500 lbs/acre and a maximum topsoil placement depth of 9 inches. Table 1 provides the carbon and nitrogen characteristics of the individual topsoil components used for the Wilson Farm blend. To achieve an adequate topsoil depth and initial organic matter content without exceeding the nitrogen loading limit, the final topsoil blend had a slightly higher than desirable C:N ratio (RMI typically targets between 35 and 45:1).
The short paper fiber and biosolids for the project were all delivered to the mixing site within a one-month period starting in July 2008, and blended into the final topsoil within one month of delivery. The sand was excavated from stratified glacial deposits on site; it was a well-sorted medium sand that was screened to 2-inch minus. Blending was accomplished using conventional construction equipment. The components were measured volumetrically, and preblended using a front-end loader. The topsoil was delivered to the Wilson Farm in dump trucks and placed, by bulldozer, at an 8-inch depth over the existing subsoil. Table 2 summarizes information on the blend and application rate.
After topsoil placement, the Wilson’s applied the recommended seed and fertilizer to the topsoil. Due to the potential for temporary nitrogen immobilization in the topsoil, the Wilson’s used inoculated clover in their seed blend and also applied a small amount of nitrogen fertilizer to give the grass/clover mix a boost of nitrogen for early growth. The amount of biosolids in the blend provided for an optimal amount of plant-available phosphorus in the final topsoil. As discussed above, it was necessary to supplement the topsoil with potassium and magnesium to provide a balance to the high calcium content of the topsoil.
Table 3 provides the trace metal content of the components of the Wilson Farm manufactured topsoil along with average values from RMI’s manufactured topsoils. With the low trace metal content of the major components of the topsoil, the sand and the short paper fiber, the final concentration of trace metals in the blended topsoil with the biosolids is very similar to the background levels of uncontaminated soils found in New England.
All of the new fields were seeded by mid-September 2008. The seed emerged within a few weeks. By June 2009, the grass/hay was coming in thick and ready for harvest. In both 2009 and 2010 the restored fields provided higher yields of hay than the other fields on the farm. Inspection reports by the DES confirmed that the project was managed according to all of the agreed upon management practices; monitoring of the surface water showed “that the topsoil application has had no effect on water quality in Warren Brook.” Interestingly, the areas of the restored fields with the poorest grass growth are the 35-foot buffer strips along Warren Brook for which some native, but low quality, topsoil was imported.
The Wilson Farm is back to where it was before the devastating floods of 2005. The only costs to the Wilson’s for restoration of the fields was the time involved in seeding and fertilizing the topsoil. RMI provided the topsoil materials, including sand, for free and paid for a portion of the work and all transportation costs. Beaudry Enterprises, a local business, donated equipment time, primarily bulldozer work for topsoil placement. And the State of New Hampshire provided permitting work for both the farm site and the blending site.
Using manufactured topsoil also eliminated the need to import natural, stripped topsoil from elsewhere. “We are back to where we can make it a farm again,” says Wilson.

Shelagh Connelly is president of Resource Management, Inc. (RMI), an organic waste recycling company. Andrew Carpenter is a soil scientist and owner of Northern Tilth and provided technical services for the Wilson Farm restoration project.

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